Electric contact



Jan. 13, 1948. E. M. wlsE ELECTRIC CONTACT Filed Oct. 12, 1943 MI QU INVENTOR.

EDMUND M. WISE BY wat 25m2 l. QQ @2SC NGE A T TORNEY.

Patented Jan. 13, 1948 ELECTRIC CONTACT Edmund Merriman wise, wesmela, N. J., assignors-.to The International Nickel Company,

lne.,

New York, N. Y., a corporation of Delaware Application October 12, 1943, Serial No. 505,967

13 Claims. (Cl. 200166 The present invention relates to electric contacts, and particularly to electric contacts which neto breakers used in circuits carrying primary y current in aircraft magnetos presented a particular problem. The opening of the breakers or contacts in an inductive circuit induces a high voltage which may approach 300 volts. Electric contacts for such applications must possess particularly high properties. They should be refractory and wear resistant. should wear smoothly and not tend to develop roughness at thecontact faces, should not tend to erode or to corrode, should exhibit low transfer or migration of metal from one contact to the opposite contact, should not tend to crater, and should not have a high contact resistance. The latter is of particular importance in magneto contacts as it largely controls the cranking speed which must be reached to produce fairly regular sparking. This is frequently referred to as the Comingin" speed. Such contacts should not show appreciable sparking or arcing in normal operation as such sparking, which develops in many magneto contact alloys operated under oily conditions, reduces the secondary voltage generated by the magneto and tends to result in uneven firing of the aircraft engine and also increases the rate of Wear of the contact. The foregoing requirements are but some of the many characteristics which must be present in satisfactory contacts.

It has been taught for years that considerable mechanical hardness was essential in electric contacts for high tension magneto service and that the very hard iridium-platinum alloy containing 25% iridium was most suitable for this purpose. It has also been recognized that platinum-containing magneto contacts failed rapidly when oil or carbonaceous gases such as gasoline vapors, hydrocarbon vapors from oil and grease, etc., were present in the breaker box and great efforts have been made to rigorously exclude' such organic materials from this region. However, as aircraft engine temperatures increase, due in part to more complete cowling, and ventilation of the breaker box becomes more difcult or perhaps impossible, at least transient exposures to carbonaceous atmospheres, i. e., oily conditions, is well nigh impossible to avoid and this is causing 2 much trouble with the conventional alloys used for aircraft magneto contacts andthe like. Good clean breaking requirements increase in importance with increased high altitude flights, particularly with supercharged engines, due to the fact that the margin between the maximum generated sparking voltage and that required to re the spark plugs drops to a low value so that alloys which do not give clean breaks cause subnormal and erratic secondary voltages, and uneven sparking at the ignition plugs. Furthermore, the vibration of the engine is seriously augmented if ignition becomes erratic. Likewise, the eifect of wear on the timing of the engine is important in maintaining a high efliciency so that the importance of contacts increases and former opinions as to satisfactory materials for such purposes have to be revised upward to higher standards and have to recognize the requirement for new properties in contact alloys to cope with changed conditions. v

My tests have shown that iridium, rhodium and ruthenium additions to platinum result in low rates of wear and generally good performance as contacts when oil vapor is not excessive and indeed the use of the ruthenium-platinum alloy containing 10% to 11% ruthenium has recently been approved by magneto and aircraft engine manufacturers who had previously standardized on an iridium-platinum alloy containing 25% iridium for contacts. In my tests I have found that the addition of palladium to platinum results in low weight losses under certain test conditions, but in long runs, for example about 1000 hours, in magnetos of current design the rates of wear as measured by loss of Weight were definitely above those of contacts made of platinums containing 25% iridium or 10 to 11% ruthenium or 14% ruthenium or 12% rhodium. In contrast to this behavior, under extremely oily conditions, which have always been considered very detrimental to platinum alloy magneto contacts, an entirely different situation prevails and the palladium-platinum aloy containing about 12% palladium becomes far superior to the others.

In view of the fact that the atmosphere within the magneto breaker is not predictable, I find that a balanced alloy is most suitable to combat the varied conditions to be met and that the aforementioned alloys are not entirely satisfactory for such purposes. I have discovered such suitable balanced compositions for electric contacts. The contacts provided by my invention aremade of an alloy which contains platinum,

an element such as palladium 'which functions well under oily conditions and another element from the group consisting of iridium, rhodium and ruthenium which are superior to palladium as an addition to platinum under low oil conditions.

It is an object of the present invention to provide an improved electric contact.

It is another object of the invention to provide an electric make and break contact made of an alloy of platinum-palladium and a member of the group consisting of iridium, rhodium and ruthenium having a special balanced composition.

It is a further object of the invention to provide an electric make and break contact particuiary adapted for use in high tension aircraft magneto circuits.

It is also an object of the invention to provide an electric make and break contact for use in ignition distributor circuits of internal combustion engines operating at least part of the time under oily conditions.

Another object of the invention is to provide an electric make and break contact exhibiting satisfactory properties when operating in the presence of hydrocarbon vapors and the like.

Other objects and advantages of the invention will become apparent to those skilled in the art from the following description taken in conjunction with the drawings in which:

Fig. 1 shows a sectional view of an aircraft magneto contact made in accordance with the invention; and

Fig. 2A and Fig, 2B are fragmentary sectional views showing the manner of constructinga multilaminar embodiment of the contacts contemplated by the present invention.

The electric contacts provided by the present invention contain about 2% to 16% palladium, about 1% to 13% of at least one metal from the group consisting of ruthenium, rhodium and iridium, and the balance substantially al1 platinum, said platinum being present in' amounts of from about 81% to 93%. In general, the alloys will fall within the range of about 5% to 14% palladium, about 2% to 11% of metal from the group consisting of ruthenium, rhodium and iridium, and the balance about 84% to 92% platinum. In the alloys provided by the present invention at least 7% of the alloy is comprised of palladium and metal from the group consisting of ruthenium, rhodium and iridium. A typical composition is one containing about 6% palladium, about 6% ruthenium and about 88% platinum but alloys in which the palladium content is as high as about 12% with the ruthenium content as low as about 2% are satisfactory particularly when oily conditions are anticipated. Under very high speed operation the corresponding rhodium-containing alloys are even better despite the fact that they are softer than the ruthenium-containing alloys. The rhodium-containing alloys and the iridiumcontaining alloys are more costly than the ruthenium-containing alloys and under normal conditions the palladium-ruthenium-piatinum alloys are entirely satisfactory. The palladiumruthenium-platinum alloys possess the added advantage that they do not require the use of iridium, which is an extremely critical metal at the present time, nor the use of rhodium, which is another rather unavailable metal at present. In comparison to the latter two metals, ruthenium is not as rare and palladium is available in still larger quantities. It is recognized, however, that for extremely long range bombing work and where the periods between overhauling are very great and where oil is expected about `the contacts the rhodium-containing platinumpalladium alloys should be employed. Where similarly long periods of use without adjustment are required but where oil will not be present much of the time, the Iridium-containing alloys have a place.

An vessential feature of the present invention is that the alloys contain not only platinum and at least one metal from the group consisting of ruthenium, rhodium and iridium, but also palladium. I have found that the presence of palladium imparts notable freedom from sparking in modern magnetos, The behavior of electric contacts under practical operating conditions is extremely complex even in the absence of oil so that any explanation of their behavior must be tentative pending further investigations, but it would appear that the beneficial effect of palladium may be due to the intermediate stability of its oxide which decomposes at temperatures above about 800 C. liberating nascent oxygen which would tend to oxidize any thin lm of organic material present on the contact and would prevent the building up of a thick oxide nlm which would tend to increase the contact resistance. During the opening of a contact in operation a certain amount of localized heating occurs and this may be sufllcient to raise the temperature at the point of break as high as the melting point and may even raise it as high as the boiling point of the contact alloy. The extent of heating should depend to a considerable extent on the thermal conductivity and the inversely related electrical resistivity. High electrical resistivity and low thermal conductivity are deemed detrimental for either oil-free or oily conditions but in the case of iridium, ruthenium and rhodium as alloy elements this is partly compensated by the increase in melting temperature occasioned by their presence. However, this is not true for palladium which does not raise the melting point. In view of this the beneficial effect of palladium in the present invention is quite unexpected.

It is a feature of the present invention that the alloys used for contact elements do not contain large proportions of' palladium or of ruthenium, rhodium or iridium. Thus an alloy containing about 7% ruthenium, about 46.5% palladium and about 46.5% platinum when tested as an electric contact in a modern magneto showed extremely poor properties even under oil-free conditions. in a 1000 hour test the wear on a contact made of such an alloy was 0.027 inch and this was almost 3 times as great as what is considered the permissible maximum wear of accepted contacts under the same test conditions. A related alloy containing 12% palladium, 15% ruthenium and 73% platinum was made and was found to crack even on hot working, Satisfactory workability is essential, of course, in this type of use as magneto contacts are made either by cutting slices from rods or by punching the contacts from sheets. The alloys provided by the present invention for use as electric contacts are ductile and can readily be worked into the desired shapes for manufacture into contacts. Furthermore, the contact alloys of the present invention possess far superior properties when used as electric contacts, for example, in aircraft magnetos. An illustrative electric contact is shown in Fig. 1 in which A is the contact surface portion made of the alloys contemplated by the invention and B is the backing or mounting portion of the contact.

Examples of some alloys within the scope of the invention, together with their Vickers hardness after working and then annealing at about 1100 C. are set forth in the following schedule as alloys 2 to 8. For comparison purposes the hardness of a specic binary palladium-platinum alloy is also included.

Per Cent Per Cent Per Cent Platinum Palladium Ruthenium Hardness 88 l2 none 61 92 6 2 108 86 12 2 120 92 2 6 191 88 6 6 191 86 2 12 l 218 Per Cent Iridium Per Cent Rhodium lAnnealed at 1300" C.

` designed to Work under high-oil and low-oil conditions. The high-oil layer may be made of a palladium-platinum alloy containing about 10% to palladium and about 80% to 90% platinum, for example about 12% palladium and about 88% platinum, and the low-oil layer may comprise an alloy containing about 6% to 14% of iridium, rhodium and/or ruthenium, and about 86% to 94% platinum, for example about 11% ruthenium and 89% platinum. The layers should be thin, preferably not over about 0.0002 inch thick, so that When the atmosphere changes from high-oil to low-oil conditions or vice versa the duration of the rapid attack on the contact Will be short and will produce little damage. In making such a multilaminar contact the multilayer material should be subjected to a diffusion treatment, either during production of the multilayer material or by a separate diffusion treatment, to obtain diffusion between the different layers. In Fig. 2A, which shows an illustrative multi-layer contact prior to diiusion treatment, C and E are alternate high-oil and low-oil thin layers (for example, about 20 to 40 layers) having the compositions indicated hereinbefore and F is the backing or mounting for the multi-layer material. Fig. 2B shows the contact of Fig. 2A after a diffusion treatment to obtain diiusion, at D, between the different layers. In this manner a multilaminar Contact is obtained having a structure comprised of regions each of which varies from the original composition of the one layer (for example, layer C) through a diiusion area (such as at D) to the original composition of the other layer (for example, layer E). In the diffusion area a zone exists having a composition within the range of the alloys described hereinbefore and comprising platinum, palladium and metal from the group consisting of rhodium, ruthenium and iridium. When the electric contact is Worn down to this zone due to changes in the conditions, the contact then possesses the surface properties of the contacts 6 hereinbefore. The multilaminar metallic ma.- terial may be produced by electrodeposition, by rolling or forging juxtaposed sheets'or plates of the dissimilar alloys or by any other suitable A method or combination of methods. A contact made of this type of material may possess advantage even in the absence of oil because of its -it is also applicable to contacts in other ignition i circuits for internal combustion engines and is suitable for contacts in relays, voltage regulators, and the like.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the present invention as those skilled in the art will understand. Thus, in addition to the metals referred to hereinbeiore, the contacts may contain small amounts of incidental elements and impurities, and it is to be understood that when it is stated that the balance is substantially all platinum, it is not intended to exclude incidental constituents and vimpurities which may be present in commercial products or which may be present in amounts not adversely affecting the desired properties of the electric contact. Again, it will be apparent that one contact made in accordance with the invention may be used in opposing another contact made of an alloy or metal of dissimilar nature, as is frequently practiced in direct current service. Such variations and modifications are considered to be Within the purview of the invention and the scope of the appended claims.

I claim:

1. As an article of manufacture, an electrical contact comprised of an alloy containing 2% to 16% palladium, 1% to 13% of a metal from the group consisting of ruthenium, iridium, and rhodium, the sum of the palladium content and the content of metal from said group being Within the range of 7% to 19%, and the balance substantially all platinum, said contact being characterized by improved service life in the presence of hydrocarbon vapors compared to a contact made of a similar palladium-free alloy.

2. As an article of manufacture, an electrical contact subjected in use to oily conditions comprised of an alloy containing 5% to 14% palladium, 2% to 11% of a metal from the group consisting of ruthenium, iridium, and rhodium, the sum of the palladium content and the content of metal from said group being within the range of 8% to 16%, and the balance substantially all platinum, said contact being characterized by improved wearing properties under oily conditions compared to a contact made of a similar palladium-free alloy.

3. As an article of manufacture, an aircraft magneto contact comprised of an alloy containing 5% to 14% palladium, 2% to 11% of one metal from the group consisting of ruthenium, iridium, and rhodium, the sum of the palladium content and the content of metal from said group being within the range of 8% to 16%, and the balance substantially all platinum, said contact being characterized by improved service life in provided by the present invention as described the presence of hydrocarbon VaPOIS COmPaJ'ed t0 tions made of an alloy containing 2% to 16% palladium, 1% to 13% of one metal from the group consisting of ruthenium, iridium and rhodium, the sum of the palladium content and the content of metal from said group being within the range of 7% to 19%, and the balance substantially al1 platinum, said contact being characterized by improved wearing properties under oily conditions compared to a contact made of a similar palladium-free alloy.

5. As an article of manufacture, an electrical contact subjected in use to oily conditions comprised of an alloy containing to 14% palladium, 2% to 11% rhodium, the sum of the palladium content and the rhodium content being within the range of 8% to 16%, and the balance substantially all platinum, said contact being characterized by improved wearing properties under oily conditions compared to a contact made of a similar palladium-free alloy.

6. As an article of manufacture, an electrical contact comprised of an alloy containing 5% to 14% palladium, 2% to 11% ruthenium, the sum of the palladium content and the ruthenium content being within the range of 8% to 16%, and the balance substantially al1 platinum, said contact being characterized by improved wearing properties under oily conditions compared to a contact made of a similar palladium-free alloy.

'7. As an article of manufacture, an electrical contact comprised of an alloy containing 5% to 14% palladium, 2% to 11% iridium, the sum of the palladium content and the iridium content being within the range of 8% to 16%, and the balance substantially all platinum, said contact being characterized by improved wearing propy erties under oily conditions compared to a contact made of a similar palladium-free alloy.

8. AS an article of manufacture, an electrical contact having a multilaminar structure comprising alternate thin layers not over about 0.0002 inch thick of an alloy containing to palladium and 80% to 90% platinum and of an alloy containing 6% to 14% of metal from the group consisting of iridium, rhodium and ruthenium and 86% to 94% platinum, said alternate thin layers being bonded to each other by a diffusion area comprising a zone having a composition within the range of 2% to 16% palladium, 1% to 13% of metal from the group consisting of ruthenium, iridium and rhodium,

and 81% to 93% platinum, the sum of the palladium content and the content of metal from said group being within the range of '1% to 19%.

9. An aircraft magneto contact comprising a1- ternate thin layers of an alloy containing 10% to 20% palladium and 80% to 90% platinum and of an alloy containing 6% to 14% of metal from the group consisting of iridium, rhodium and ruthenium and 86% to 94% platinum, said alternate layers being bonded to each other by a diiusion zone comprising platinum, palladium and said metal from said group.

10. An electrical contact comprised of a ductile alloy containing about 6% palladium, 6% of a metal from the group consisting of ruthenium, Iridium and rhodium and the balance substantially all platinum, said contact being characterized by improved service. life when operated in hydrocarbon atmospheresy compared to a contact made of a similar palladium-free alloy.

11. An aircraft magneto contact subjected in use to oily conditions comprised of a ductile alioy containing about 6% palladium, 6% ruthenium and 88% platinum, said contact being characterized by improved service life under oily conditions compared to a contact made of a similar palladium-free alloy.

12. An aircraft magneto contact subjected in use to oily conditions comprised of a ductile alloy containing about 6% palladium, 6% rhodium and 88% platinum, said contact being characterized by improved service life under oily conditions compared to a contact made of a similar Dalladium-free alloy.

13. An aircraft magneto contact subjected in use to oily conditions comprised of a ductile alloy containing about 6% palladium, 6% iridium and 88% platinum, said contact being characterized by improved service life under oily conditions compared to a contact made of a similar Dalladium-free alloy.

EDMUND MERRIMAN WISE.

REFERENCES CITED The following references are of record in the l file of this patent:

u UNITED STATES PATENTS Number Name Date 1,779,602 Kingsbury Oct. 28, 1930 2,300,286 Gwyn, Jr. Oct. 29, 1942 1,339,505 Fahrenwald May 1l. 1920 

